The epidermal growth factor receptor (EGFR) is overexpressed in 90% of head and neck squamous cell carcinoma (HNSCC), and is correlated with poor prognosis. EGFR is therefore a potential therapeutic target for HNSCC. However, most HNSCC patients do not respond well to small molecular EGFR inhibitors. One of the possible mechanisms of EGFR TKI resistance is compensatory collateral activation of PI3K/Akt pathway. This study sought to explore whether NVP-BKM120, a selective pan class I PI3 kinase inhibitor, and NVP-BYL719, a novel PI3 kinase alpha selective inhibitor, may reverse the resistance of HNSCC cells toward erlotinib, an EGFR TKI. Cells were treated with the PI3K inhibitors, either BKM120 or BYL719, alone, erlotinib alone, or in combination, and viability was measured at 72 hours with MTT assay. Combination effect was evaluated by median effect analysis. Synergism, indicated by a combination index (CI) value <1, were seen in all five cell lines (SAS, HSC3, UMCC1, CA922 and FaDu) studied. By immunoblotting analysis, combination of Erlotinib and either PI3K inhibitor resulted in dowregulation of p-EGFR and p-AKT expression in SAS cells. When SAS and HSC3 cells were treated with erlotinib in combination with either BKM120 or BYL719, an additional increase in the subG1 population by flow cytometry analysis were observed, indicating an increase of apoptotic cell death. Our data suggest that additional PI3K blockade might be an effective strategy to overcome resistance of HNSCC cells toward EGFR TKIs, and the beneficial effect is similar between pan Class I PI3K inhibitor and PI3K alpha selective inhibitor. (The study was supported by the grant of DOH101-TD-B-111-001).

Citation Format: Ming Gao, Yen-Shen Lu, Li-Ping Hsiao, Suz Wen Chen, Ann-Lii Cheng. Either pan class I PI3K inhibitor or PI3K alpha selective inhibitor sensitizes head and neck squamous cell carcinoma cells to Erlotinib, an EGFR TKI. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2450. doi:10.1158/1538-7445.AM2013-2450